Differential gear for watch movement

ABSTRACT

A differential gear for watch movement may include a central shaft whereon first and second wheels are rotatably mounted, each of which is provided with a toothing arranged to mesh with a toothing of at least one satellite borne by a satellite carrier also mounted on the central shaft. The first and second wheels may be configured to engage first and second mobiles of the watch movement, the central shaft including a toothing configured to engage a third mobile of the watch movement. Further, the satellite carrier may be secured in rotation with the central shaft by a friction device comprising a tube having a first portion arranged bearing against the central shaft and at least one second portion arranged bearing against the satellite carrier. The tube may include a substantially cylindrical skirt, wherein at least one first tab is formed in such a way that it exerts a force having a radial component on the satellite carrier.

The present application claims the priority of European (EP) PatentApplication No. 09162837.0, filed on Jun. 16, 2009. The disclosure of EP09162837.0 is expressly incorporated herein by reference to itsentirety.

TECHNICAL FIELD

The present disclosure relates to a differential gear for a watchmovement including a central shaft whereon first and second wheels arerotatably mounted, each of which is provided with a toothing arranged tomesh with a toothing of at least one satellite borne by a satellitecarrier, also mounted on the central shaft. The first and second wheelsmay be configured to engage first and second mobiles of the watchmovement, the central shaft including a toothing configured to engage athird mobile of the watch movement.

In particular, and without limitation, the present disclosure relates toa differential gear of this type intended to control a display mechanismof a running reserve of a barrel spring in a timepiece including abarrel as a motor organ.

The present disclosure also relates to a watch movement provided withsuch a differential gear, in particular for controlling a displaymechanism of the running reserve, as well as a timepiece provided withsuch a watch movement.

BACKGROUND

Differential gears are commonly used in watch movements with automaticor manual rewinding.

By way of example, patent CH 263 707, published on Dec. 1, 1949,describes a differential gear for the displaying of the running reserveof a watch.

This differential gear includes two large wheels provided, on the onehand, with radial toothings connected kinetically to one end and theother of the barrel spring and, on the other hand, with contratetoothings configured to engage a satellite having the form of aconventional pinion. The differential gears of this type are cumbersomein terms of their thickness and are therefore not used very often inwristwatches.

Moreover, a general problem with mechanisms with running reserveindication is management of a value to be displayed when the spring ofthe barrel is fully rewound, either through an automatic windingmechanism, or through manual winding. If the winding is continued, thebarrel generally includes a slip-spring in order to prevent anypotential damage, while a display mechanism of the running reserveincludes a stop at a location or otherwise in order to prevent a displaymember from turning further. However, a wheel of the differential gearis connected kinetically to a barrel drum which continues to turn duringthe winding, even when the spring has been fully wound. It is thereforedesirable to provide a system for preventing the gears involved in thedisplay of the running reserve from any damage, in these conditions.

The above-mentioned patent proposes to mount one of the wheels of thedifferential gear on its shaft with a viscous friction in order to allowit to slide on the shaft when the barrel spring has been fully wound.

Note that such a measure further makes it possible to be free of therequirement of providing a pairing for the placing of the memberindicating the running reserve due to the fact that its position can beadjusted by means of the stop mentioned above.

Patent application EP 1 139 182 A1, published on Oct. 4, 2001, proposesan alternating differential gear, implementing gears of a conical type,less cumbersome than those described above. Furthermore, that patentapplication proposes a solution, making it possible to take into accountthe situation put forth hereinabove, consisting in inserting a specific,but complex, mobile, between the differential gear and the mobile fordisplaying the running reserve.

SUMMARY

The present disclosure proposes an improved differential gearincorporating a safety against risks linked to excessive winding of abarrel spring, while still having a structure that is simple and notvery cumbersome. Embodiments of the present disclosure may also relateto such a differential gear including a safety against similar riskswhen it is implemented in a mechanism other than a display mechanism ofthe running reserve.

The present disclosure also relates to a differential gear of the typementioned above, having a satellite carrier that may be rendered securedin rotation to a central shaft by the intermediary of a friction deviceincluding a tube having a first portion arranged bearing against thecentral shaft and at least one second portion arranged bearing againstthe satellite carrier.

It is contemplated that the tube may include a substantially cylindricalskirt, wherein at least one first tab may be formed in such a way thatit exerts a force having a radial component on the satellite carrier,which may be centripetal or centrifuge according to alternativeembodiments. Furthermore, the skirt may include at least one additionaltab, of a length slightly greater than that of the first tab, in orderto define a positioning stop of the tube in relation to a shoulder ofthe central shaft.

With these characteristics, a specific and separate mechanism forpreserving the gears is not required in that such a mechanism isincorporated directly into the differential gear. The differential gear,despite this direct incorporation, retains very reasonable dimensions,due to the judicious arrangement of the friction tube.

The tube may also have a base provided with an edge forming an axialretention for one or more wheels.

Moreover, in order to limit the entire space occupied by thedifferential gear according to the present disclosure, the satellite maybe provided with a toothing of a sliding pinion type arrangedsimultaneously in mesh with the toothings of first and second wheels,the first and second wheels being radial.

The present disclosure also relates to a watch movement incorporating adifferential gear having the characteristics described above, with themovement including a barrel housing a barrel spring of which a first endis connected kinetically to a going train and a second end is connectedkinetically to a device for rewinding, the differential gear beingarranged to control a display mechanism of a running reserve of thebarrel spring.

Additional objects and advantages of the present disclosure will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of thepresent disclosure. The objects and advantages of the present disclosurewill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present disclosure, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentdisclosure and together with the description, serve to explain theprinciples of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present disclosure shall appear more clearly whenreading the detailed description which follows, provided in reference tothe annexed drawings given by way of non-restrictive examples, andwherein:

FIG. 1 shows a cross-sectional perspective view of a differential gear,according to an aspect of the present disclosure;

FIG. 2 shows a simplified perspective view of an element of thedifferential gear of FIG. 1;

FIG. 3 shows a simplified cross-section view of the element of FIG. 2;

FIG. 4 shows a simplified perspective view of a portion of thedifferential gear of FIG. 1 showing certain construction details, and

FIG. 5 shows a perspective view of an element of a differential gear,according to another aspect of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 shows a cross-sectional perspective view of a differential gear 1according to an aspect of the present disclosure. More precisely,approximately a front half of differential gear 1 has been removed inorder to show its internal structure.

Differential gear 1 includes a central shaft 2 configured to allow formounting on a frame element of a watch movement, shaft 2 being providedwith a pivot on each of its ends 3 and 4.

A terminal pinion 5 may be solid with the central shaft in the vicinityof one of its ends 3. Alternatively, the pinion may be formed separatelythen added. The pinion is followed by a cylindrical support portion 6,which itself is followed by a main portion 7 of shaft 2, alsocylindrical but of a smaller diameter and extending to the other end 4of shaft 2.

A first input wheel 8 of differential gear 1, borne by a hub 9, isarranged bearing on support portion 6, and is retained axially by pinion5. Hub 9 includes a base, wherein a radial toothing 10 is arranged, thebase being overmounted with a pipe 11 whereon first wheel 8 is driven.

The length of support portion 6 is very slightly greater than the heightof hub 9.

An intermediate tube 12 is then engaged on main portion 7 of centralshaft 2, covering it substantially to the second end 4 of shaft 2. Thestructure of tube 12 will be described in detail, with reference beingmade to FIG. 2 and FIG. 3 where appropriate. It already appears in FIG.1, according to the transversal cross-section view of tube 12, that tube12 has a base 14 provided with an annular edge having the form of aretaining ring 15, followed by a support portion 16, having asubstantial material thickness, and itself followed by a main portion17, or skirt, which is thinner and extends to a shoulder 18 of centralshaft 2, defined by the junction between support portion 6 of shaft 2and its main portion 7.

Before the setting in place of tube 12 on central shaft 2, a satellitecarrier 20 is engaged on main portion 17 of tube 12.

Satellite carrier 20 includes first and second coaxial rings 21, 22,connected together by a flange 24. Moreover, a shaft 25 is borne byrings 21, 22, following a direction perpendicular to the direction ofcentral shaft 2, and carries a satellite 26.

Satellite carrier 20 further performs the function of retaining for asecond input wheel 28 of the differential gear, engaged beforehand onsupport portion 16 of tube 12.

In a manner similar to first wheel 8, second input wheel 28 is borne bya hub 29 including a base, wherein a radial toothing 30 is arranged, thebase being overmounted with a pipe 31 whereon second wheel 28 is driven.Hub 29 is, on one side, arranged thrust against retaining ring 15 and,on another side, retained by satellite carrier 20.

Hubs 9, 29 are arranged in opposite directions, such that theirtoothings are across from one another, in such a way as to be able tocooperate with satellite 26.

Conventionally, one of the wheels is connected kinetically to a firstend of a barrel spring, either by an intermediary of a barrel drum or ofa barrel shaft, while the other wheel is connected kinetically toanother end of the barrel spring. As such, in a known manner, thechanges in the state of the winding of the barrel spring, according tothe normal operation of the corresponding timepiece or of possibleoperations of manual or automatic winding, are taken into account inorder to be transmitted to a display mobile of the running reserve,starting from the exit of differential gear 1, or terminal pinion 5.

Note that input wheels 8, 28 turn in opposite directions in order todrive satellite carrier 20 in respective opposite directions ofrotation.

FIG. 2 shows a simplified perspective view of the isolated tube 12 andmakes it possible to better discern its structure, more particularlythat of its main portion 17.

Main portion 17 may have a general cylindrical shape, and may includetwo pairs of tabs 34, 35, two tabs of the same pair being diametricallyopposite in relation to the axis of tube 12.

A pair of long tabs 34 may be configured to act as positioning stopswhen tube 12 is engaged on central shaft 2, as has already beenmentioned above.

The free ends of tabs 34, 35 all have an allowance such that thediameter of main portion 17 of tube 12, on free ends of tabs 34, 35, issimilar to the diameter of the opposite end of main portion 17, i.e.that which is connected to support portion 16. This diameter correspondssubstantially to the internal diameter of ring 21 of satellite carrier20, such as is shown in FIG. 1.

As such, satellite carrier 20 is adjusted on tube 12. However, theparticular structure of main portion 17 of tube 12 provides it withelastic properties, in particular by deformation of tabs 35, which allowfor a relative sliding between tube 12 and satellite carrier 20 when thetorque to be transmitted between these elements exceeds a predefinedvalue reached when the barrel spring becomes fully wound. Below thispredefined value, tabs 35 exert a force having a radial component,centrifugal here, on satellite carrier 20, such that these two elementsare secured in rotation.

The fact that short tabs 35 are not thrust against central shaft 2allows for a better control of their contribution in the definition ofthe value of maximum torque desired before sliding.

FIG. 3 shows a simplified cross-section view of tube 12 in FIG. 2,wherein various configurations of tabs 35 have been diagrammed, in orderto show in what manner their degree of deformation can be adjustedaccording to the force desired to act on satellite carrier 20.

FIG. 4 shows a simplified perspective view of a portion of differentialgear 1 in FIG. 1 showing certain construction details. More precisely,first input wheel 8 has been removed in order to show more clearlysatellite carrier 20 and satellite 26 according to this embodiment ofthe present disclosure.

FIG. 4 shows that flange 24 connecting first and second rings 21, 22 hasa plurality of openings 40, in particular to lighten it. Of course, itis possible to provide, alternatively, that arms are used to connectfirst and second rings 21, 22 to one another instead of flange 24.

Moreover, flange 24 includes an additional opening 41 wherein asatellite 26 is housed, borne by shaft 25.

It also appears in FIG. 4 that satellite 26 has a particular shape, i.e.it is similar to that of a sliding pinion, used in winding mechanisms,wherein conventional Breguet teeth have not been cut.

As such, satellite 26 includes a toothing 42 of the sliding pinion type,i.e. a contrate toothing oriented according to a direction that issubstantially parallel to the axis of rotation of satellite 26 by havinga symmetry according to this axis. Thanks to this characteristic,satellite 26 can mesh with conventional radial toothings, which arethose borne by hubs 9 and 29 in the embodiment shown in FIG. 4.Therefore, the space occupied by differential gear 1 is reduced in thedirection of height in relation to a conventional differential gearwherein the satellite has the shape of a conventional pinion with radialtoothing.

Moreover, satellite 26 includes an annular groove 43 configured tocooperate with fingers 44 arranged in flange 24 of satellite carrier 20in order to ensure a good positioning of satellite 26 in relation tosatellite carrier 20, therefore in relation to the first and secondinput wheels 8 and 28.

The view in FIG. 4 shows more particularly that not only theconstruction of differential gear 1 has a space that is reduced in thedirection of the thickness and a simplified assembly in relation to thegears of prior art, but furthermore it makes it possible to procuregreat stability for satellite 26 on its shaft 25 due to the substantiallength of these two elements.

FIG. 5 shows a perspective view of a central shaft 60, according to analternative embodiment, intended to cooperate with a tube as describedabove.

Central shaft 60 includes a tapered portion 61 configured to cooperatewith the ends of tabs 35, the ends of tabs 35 having to be deformed inthe direction of the interior and no longer to the exterior as was thecase in the previous embodiment. Therefore, the tube exerts acentripetal force on central shaft 60 in order to produce an effect thatis similar to that mentioned above. The tube is, in this case, securedin rotation with the satellite carrier.

Note that, in one case as in the other, the friction force F providingthe transmission of the movements of rotation of the tube to thesatellite carrier (in the first case) or to the central shaft (in thesecond case) can be expressed as being equal to the product of μ by N,where μ is the coefficient of friction, depending on the two materialsin contact with one another, and N is the radial force exerted by thetube on the satellite carrier or on the central shaft due to thedeformation of its tabs 35. The particular structure of the tube allowsfor a relatively precise adjustment of the value of N, μ being knownfrom the moment when the materials involved have been selected. As suchthe value of F, directly linked to the moment of force implied betweenthe two elements in contact, can be adjusted in a relatively precisemanner (the moment being equal to the product of F by the radius at thepoint of application of F, or the point of contact between the twomembers involved).

Consequently, the threshold value of the moment of force with which thetube starts sliding in relation to the other member involved can beadjusted to be close to the value required for the transmission of themoments of force required to provide for the proper operation of thecorresponding watch mechanism, which makes it possible to reduce thewear and tear of the parts linked to the friction, compared to themechanisms known in prior art. Further note that if the tabs 35 aredeformed excessively in a given direction, they can be brought back inthe opposite direction, possibly in a reversible manner according to thenature of the material used.

The description above focuses on describing particular embodiments forthe purposes of providing non-restricted examples. The presentdisclosure should not be restricted to the implementation of certainparticular characteristics which have just been described, as forexample the shape specifically shown and described of the satellitecarrier, the embodiment shown of the input wheels or that of the centralshaft. As such, by way of example, note that terminal pinion 5 may bereplaced with a toothing arranged directly on the periphery of retainingring 15 of tube 12. Likewise, it can be considered to carry out only twotabs in the tube, of which a single exerts a force with radial componenton the satellite carrier or on the central shaft in order to provide thefunction of friction, while the other provides for the positioning ofthe tube on the central shaft and/or the guiding of the satellitecarrier.

Those skilled in the art will not encounter any particular difficulty inadapting the content of this disclosure to their own needs andimplementing a differential gear that is different from that accordingto the embodiments described here, but wherein the satellite carrier isrendered secured in rotation with the central shaft by the intermediaryof a friction device including a tube having a first portion arrangedbearing against the central shaft and at least one second portionarranged bearing against the satellite carrier, without leaving thescope of the present disclosure. Note also that the differential gear ofthe present disclosure can also be implemented in watch mechanisms otherthan those intended to display the running reserve.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the embodiments disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the present disclosure being indicated by thefollowing claims.

1. A differential gear for a watch movement, comprising: a central shaftwhereon first and second wheels are rotatably mounted, each of which isprovided with a toothing arranged to mesh with a toothing of at leastone satellite borne by a satellite carrier also mounted on said centralshaft, said first and second wheels being configured to engage first andsecond mobiles of the watch movement, said central shaft comprising atoothing configured to engage a third mobile of the watch movement, saidsatellite carrier being secured in rotation with said central shaft by afriction device comprising a tube having a first portion arrangedbearing against said central shaft and at least one second portionarranged bearing against said satellite carrier.
 2. The differentialgear of claim 1, wherein said tube further comprises a substantiallycylindrical skirt, at least one first tab being formed in such a waythat it exerts a force having a radial component on said satellitecarrier.
 3. The differential gear of claim 2, wherein said skirtcomprises at least one additional tab, of a length slightly greater thanthat of said first tab, defining a positioning stop of said tube inrelation to a shoulder of said central shaft.
 4. The differential gearof claim 1, wherein said tube has a base provided with an edge formingan axial retention for one of said first and second wheels.
 5. Thedifferential gear of claim 2, wherein said tube has a base provided withan edge forming an axial retention for one of said first and secondwheels.
 6. The differential gear of claim 1, wherein said satellite hasa sliding pinion type toothing arranged simultaneously in mesh with saidtoothings of said first and second wheels, the toothings of said firstand second wheels being radial.
 7. The differential gear of claim 2,wherein said satellite has a sliding pinion type toothing arrangedsimultaneously in mesh with said toothings of said first and secondwheels, the toothings of said first and second wheels being radial. 8.The differential gear of claim 4, wherein said satellite has a slidingpinion type toothing arranged simultaneously in mesh with said toothingsof said first and second wheels, the toothings of said first and secondwheels being radial.
 9. The differential gear of claim 6, wherein saidsatellite carrier comprises two coaxial rings, said satellite beingmounted in rotation on a shaft having ends borne by said rings.
 10. Thedifferential gear of claim 6, wherein said satellite has a peripheralgroove coaxial to an axis of rotation of said satellite, and saidsatellite carrier comprises at least one finger configured to engagesaid groove, in the service position of said satellite, in order toensure the positioning of the satellite.
 11. The differential gear ofclaim 9, wherein said satellite has a peripheral groove coaxial to anaxis of rotation of said satellite, and said satellite carrier comprisesat least one finger configured to engage said groove, in the serviceposition of said satellite, in order to ensure the positioning of thesatellite.
 12. The differential gear of claim 1, wherein said first andsecond wheels are connected kinetically respectively to first and secondends of a barrel spring, said central shaft being connected kineticallyto a display mechanism of a running reserve of the barrel spring. 13.The differential gear of claim 2, wherein said first and second wheelsare connected kinetically respectively to first and second ends of abarrel spring, said central shaft being connected kinetically to adisplay mechanism of a running reserve of the barrel spring.
 14. Thedifferential gear of claim 4, wherein said first and second wheels areconnected kinetically respectively to first and second ends of a barrelspring, said central shaft being connected kinetically to a displaymechanism of a running reserve of the barrel spring.
 15. Thedifferential gear of claim 6, wherein said first and second wheels areconnected kinetically respectively to first and second ends of a barrelspring, said central shaft being connected kinetically to a displaymechanism of a running reserve of the barrel spring.
 16. Thedifferential gear of claim 9, wherein said first and second wheels areconnected kinetically respectively to first and second ends of a barrelspring, said central shaft being connected kinetically to a displaymechanism of a running reserve of the barrel spring.
 17. A watchmovement, comprising: a differential gear comprising a central shaftwhereon first and second wheels are rotatably mounted, each of which isprovided with a toothing arranged to mesh with a toothing of at leastone satellite borne by a satellite carrier also mounted on said centralshaft, said first and second wheels being configured to engage first andsecond mobiles of the watch movement, said central shaft comprising atoothing configured to engage a third mobile of the watch movement, saidsatellite carrier being secured in rotation with said central shaft by afriction device comprising a tube having a first portion arrangedbearing against said central shaft and at least one second portionarranged bearing against said satellite carrier.
 18. The watch movementaccording to claim 17, comprising a barrel housing, a barrel spring ofwhich a first end is connected kinetically to a going train and a secondend is connected kinetically to a device for rewinding, saiddifferential gear being arranged to control a display mechanism of arunning reserve of said barrel spring.
 19. A timepiece provided with awatch movement, comprising: a differential gear including a centralshaft whereon first and second wheels are rotatably mounted, each ofwhich is provided with a toothing arranged to mesh with the toothing ofat least one satellite borne by a satellite carrier also mounted on saidcentral shaft, said first and second wheels being configured to engagefirst and second mobiles of the watch movement, said central shaftcomprising a toothing configured to engage a third mobile of the watchmovement, said satellite carrier being secured in rotation with saidcentral shaft by a friction device comprising a tube having a firstportion arranged bearing against said central shaft and at least onesecond portion arranged bearing against said satellite carrier.
 20. Thetimepiece of claim 19, comprising a barrel housing a barrel spring ofwhich a first end is connected kinetically to a going train and a secondend is connected kinetically to a device for rewinding, saiddifferential gear being arranged to control a display mechanism of arunning reserve of said barrel spring.